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Old 13-03-2012, 21:21   #1
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Cost Effectiveness AGM vs. Flooded Cell

I'm cruising the Caribbean right now and am currently in Luperon. I will have to make the trip back to the Florida Keys in the next two month. When I get back to the Keys I plan on replacing both my battery banks. So I have been doing a lot of research on agm vs flooded cell and decided to make a small spread sheet with my observations. I would greatly appreciate any feedback and constructive criticism, attached is my spread sheet in pdf format.


Thank You
Chris
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File Type: pdf AGM vs. Wet Cell PDF.pdf (62.5 KB, 243 views)
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Old 13-03-2012, 21:50   #2
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Re: Cost effectiveness AGM vs. Flooded Cell

A few points from my perspective:

I think even overall the Wet cells are cheaper as you not may achieve full cycles numbers if you are not able to charge back to 100% on a regular base.
I did a lot of research on myself as well in the past - and to put it in simple words: I strongly believe Wet is cheaper for a typical "off the hook" cruiser.

Charging the batt's up to 100% regularly and equalize (even AGMs) from time to time is the only way to achieve long live. If not it speaks again for wet.
Other questions would be if your current setup is ready for AGM or needs additional $$. If not again wet :-)

Nevertheless saying all that: I personally went with AGM and a big solar array to charge them 100% almost daily. Mainly because of less maintenance and therefore comfort. I'm happy but it was not a 100% money driven decision - and I guess cost was your original question.
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Old 13-03-2012, 22:17   #3
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Re: Cost effectiveness AGM vs. Flooded Cell

These were just some observations I had made and was curious if there were at all correct. My boat has 400 Watts of solar with a ts-60 charge controller. With my current setup I have to run my engine about 1 to 2 hours a day. My major problem is that I'm a bit of a techy and there for I use a lot of power, around 250 to 300 amps per day. I have 8 golf cart batts. on 2 separate banks with a total 860ah and a separate start bank. I was hoping that with agm batteries I wouldn't have to run my engine as much and my solar would be a bit more effective. Mabey thats just wishful thinking.
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Old 13-03-2012, 22:18   #4
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Re: Cost effectiveness AGM vs. Flooded Cell

My $0.02 is that on paper agm is great but for the rather miserable treatment that marine batteries are exposed to the versatility and tolerance for problems makes wet cells a "better" investment. If you're an electrogeek and you're super into your electrical system that's one thing. But if you're some guy with a multimeter who wants to have a pretty brain dead and effective system maybe go with lead acid.
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Old 13-03-2012, 22:21   #5
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Re: Cost effectiveness AGM vs. Flooded Cell

Quote:
Originally Posted by topsideup View Post
These were just some observations I had made and was curious if there were at all correct. My boat has 400 Watts of solar with a ts-60 charge controller. With my current setup I have to run my engine about 1 to 2 hours a day. My major problem is that I'm a bit of a techy and there for I use a lot of power, around 250 to 300 amps per day. I have 8 golf cart batts. on 2 separate banks with a total 860ah and a separate start bank. I was hoping that with agm batteries I wouldn't have to run my engine as much and my solar would be a bit more effective. Mabey thats just wishful thinking.
Just for a comparison I have 270 watts of solar and use maybe 100-150 amps per day. So I'm at half your usage but I have about 20% more solar than you. Engine goes on (for battery purposes) if the weather is cloudy for a couple of days.
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Old 13-03-2012, 22:32   #6
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Re: Cost effectiveness AGM vs. Flooded Cell

I monitor my system closely with a Xantrax link 10 pro. I rarely let my banks fall below 60% of capacity. Doing this I have got 6 good years of life out of my banks so far. O I also forgot to mention that I am a full time liveabored.
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Old 13-03-2012, 23:09   #7
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Re: Cost effectiveness AGM vs. Flooded Cell

G'day, mate. Well over a decade now on our original Lifeline AGM's living roughly 60% on the hook and still have some cycles left. We certainly have not missed the mainteance issues associated with the wet cells. We have consistently equalized our AGM's over the years according to Lifelines specifications. When we do need to replace them, it will most definitely be with AGM's again.

I really don't think you are going to get any significant reduction in engine running time if you do switch. You may want to look at getting another panel. All the best. Cheers.
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Old 13-03-2012, 23:20   #8
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Re: Cost effectiveness AGM vs. Flooded Cell

I thought that AGM batteries have lower internal resistance and could accept anywhere between 40% to 45% of total AH when charging. that was my thought process for having less engine run time.
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Old 14-03-2012, 02:06   #9
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Re: Cost effectiveness AGM vs. Flooded Cell

Quote:
Originally Posted by topsideup View Post
I thought that AGM batteries have lower internal resistance and could accept anywhere between 40% to 45% of total AH when charging. that was my thought process for having less engine run time.
Yes thats correct, I think my lifelines have even more, but not sure. I have a 600 Amp bank and since my Balmar is "just" 120A max I never hit more than 20% - Ok the solar may add another 5% or so but still way off the limit. In any case reduce the charging amps if you the same we do: As soon the engine runs we run the inverter for charging laptops and whatever madam needs...
Not sure about about your setup, but if you have a 2-400 Amp Alternator on your engine: That rock's!!!

If you really stick with 250 - 300 Amps per day and its mostly 12 V I would think about a DC Genset - or an AC with a BIG Charger if its more AC & DC.

But thats all more or less guessing. We do not really have an idea about the current setup/need. If you rethink the batt's Its maybe as well time to rethink the setup in general. Make the great sheet you did for the batt's as well in the classical way: Power usage, saving potential vs. DC production. Maybe some new ideas there!

Good Luck!
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Old 14-03-2012, 02:54   #10
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Re: Cost effectiveness AGM vs. Flooded Cell

Quote:
Originally Posted by topsideup View Post
I thought that AGM batteries have lower internal resistance and could accept anywhere between 40% to 45% of total AH when charging. that was my thought process for having less engine run time.
Lifeline AGMs can accept up to 500% of their Ah capacity - that's 500 amps for a 100 Ah battery - totally impractical but it is one reason they can charge much more quickly. Like all batteries their charge acceptance rate declines as the charge level increases.

Because of their low resistance they are also much more efficient at charging. Wet cells are only 85% efficient which means that 115 Ah or more must be put in to actual raise the capacity of a 100 Ah battery by 100%. AGMs may be 98% efficient so only 102 Ah need to be put in. So faster charging even without changing the size of your chargers. If you increase your charging capability then you will achieve even faster charging - and less engine or genset runtime.

We have a Fischer Panda DC genset that pumps out a maximum of 280 amps. This is a very good option for AGMs.
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Old 14-03-2012, 04:31   #11
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Re: Cost effectiveness AGM vs. Flooded Cell

My feeling is that unless you upgrade your alternator to take advantage of the higher charging acceptance rate that paying more for AGMs is a waste. And once you have the AGMs you HAVE to charge them fully for they won't last.

For the price, life, use, punishment they can take it's hard to beat wet cells. All at the small price of checking the water once in a while.
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Old 14-03-2012, 04:53   #12
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Re: Cost effectiveness AGM vs. Flooded Cell

That information in your chart is missing the most important aspect of battery longevity and that is EQUALIZING. The total life of a battery is achieved by negating the sulfation that occurs in lead acid batteries as they mature. Reversal of sulfation will lead to extended battery life and better overall performance.
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Old 14-03-2012, 06:28   #13
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Re: Cost Effectiveness AGM vs. Flooded Cell

Our Deka AGM house bank (2 8A31DT's, 105AH each, for a total of 210AH) completed its eleventh summer cruising BC and SE Alaska last year, anchoring overnight most of the time.

We have no genset, no solar panel, and do not equalize. We do have a proper charging system - Balmar 75A alternator, MC-612 regulator, and Link 2000 monitor. We generally discharge down no lower than 50%, and recharge while traveling under power. Two hours of travel (even at only 6 knots, our typical speed) generally brings the charge up more than adequately.

I was considering running these batts again this summer, but replaced them with a new pair of 8A31DTM's ($197 each from an industrial battery supplier) just to be on the safe side.

The boat diesel's Optima AGM starting bank lasted 7 years, after which I replaced with Deka 9A34M AGM's. The Optima's in our diesel truck - no special charging system there - finally got too weak this winter after ten years. They would start the truck reliably after sitting for 3 months while we were cruising every summer. Replaced them with Deka 9A34M's as well.

I figured it cost a little less than $100/year for the total of all six of these batteries.
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Old 14-03-2012, 07:39   #14
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Re: Cost Effectiveness AGM vs. Flooded Cell

Topsideup-
Your analysis is the basis for an excellent discussion that should lead to the "right" decision for you.

A couple of points:
1. There is one fundamental error in your analysis:
Quote:
Also the charging rating is bases on a single 12v battery or 2 6 volts in series
As I am sure you know, when two 6VDC batteries are in series the amp-hr rating of the two batteries does not change. The result is a 12VDC battery with an amp-hr rating of a single battery in the pair.
2. The Trojan site currently states that, for FLA batteries, the charging rate should be 10% to 13% of the battery's 20 hr rate. Two T105s can therefore accept as much as 0.13 x 225 = 29.25 amps not the 56.25 amps in your tabulation. These corrections will significantly change your calculations. (It should be noted that, over the last ten years the maximum charging rate for T105s has steadily dropped from 0.25C to 0.17C and now to 0.13C)
3. I searched the entire Trojan site for the maximum charging current that their AGMs will accept to no avail. I have sent an email to their tech support requesting this info. That said, most AGMs will accept from 0.7C to 0.8C and many can accept well above 1C. Your charge rate for AGMs must be adjusted to the correct value in order to perform a valid comparison as this is one of the biggest advantages of AGMs over FLA.
4. Nigel Calder has given seminars regarding the true, amortized cost of recharging using a genset or an alternator to charge a battery bank. As I recall it was extremely high...dollars per amp-hr. I will try and find the source document.

As a general note; few of the AGM battery manufacturers recommend equalizing their batteries with Lifeline a notable exception.

Charlie
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Old 14-03-2012, 09:47   #15
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Re: Cost Effectiveness AGM vs. Flooded Cell

I believe Lifeline is the only AGM vendor suggesting equalization. Not sure if this was added after too many short lived batteries got returned for warranty. While AGMs will take a higher charge thus shortening the charge time, you have to also take into account the need to get the batteries to 100% charge state periodically. How long is periodically? Maybe once or twice a week. Charging from 85% to 100% is still slow.
I've had AGMs on board for 3 years. The first set died a premature death after one year -- crap for manufactuer support. These were charged with a quality charger -- just bad batteries that were overspec'd by the vendor. Now have Victron AGMs for the last 2 years, full time liveabord. Still working great. I use AGMs primarily because I can fit them in on their side in the space I have.
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